Walmart said Thursday it's investigating a photo that's attracted interest on social media by purporting to show a sign reading "Own The School Year Like A Hero" atop a gun-filled case in one of the company's stores.

The sign is apparently one that's used in Walmart's current superhero-themed "back to school" marketing campaign, but the company said in a statement that "what's seen in this photograph would never be acceptable in our stores."

Walmart spokesman Charles Crowson said the company hasn't determined which store might have displayed the sign above guns, or even if the photo is real.

The photo showing the "Own The School Year" sign atop a six-sided glass display case filled with rifles has attracted attention on social media, drawing comments of outrage and mentions of school shootings.

Crowson said Walmart is "exploring all possibilities," including whether an employee unintentionally erected the sign, if it's a prank, or if the image was edited to show something that doesn't exist.

He said Walmart believed early Wednesday that the photo was taken inside one of its Evansville, Indiana, stores after speaking to a person who said they posted the photo online. But Crowson said a comparison of photos and video of the sporting goods departments in the company's two Evansville stores that sell firearms showed it wasn't taken inside either one.

"We're still trying to track down which store it is," he said. "We are all working right now to positively identify this as quickly as possible."